Tire non-uniformity relates to the symmetry (or lack of symmetry) relative to the tire's axis of rotation in certain quantifiable characteristics of a tire. Conventional tire building methods unfortunately have many opportunities for producing non-uniformities in tires. During rotation of the tires, non-uniformities present in the tire structure produce periodically-varying forces at the wheel axis. Tire non-uniformities are important when these force variations are transmitted as noticeable vibrations to the vehicle and vehicle occupants. These forces are transmitted through the suspension of the vehicle and may be felt in the seats and steering wheel of the vehicle or transmitted as noise in the passenger compartment. The amount of vibration transmitted to the vehicle occupants has been categorized as the “ride comfort” or “comfort” of the tires.
Tire uniformity characteristics, or attributes, are generally categorized as dimensional or geometric variations, mass variance, and stiffness variations. Common measurements for assessing tire uniformity include geometric variation measurements (e.g. radial run out and lateral run out) and force variation measurements (e.g. radial force variation, lateral force variation and tangential force variation, sometimes also called longitudinal or fore and aft force variation). Uniformity measurement machines often measure the above and other uniformity characteristics by measuring force and/or geometry at a number of points around a tire as the tire is rotated about its axis.
Cavity noise in tires can be generated by the excitation of the air contained inside a closed tire cavity. When cavity noise appears when a tire is rolling on a smooth surface (e.g. during performance tests), the excitation of the air contributing to the cavity noise can be caused at least in part by tire non-uniformity, such as radial run out of the tire. For instance, a localized peak of radial run out of a tire caused, for instance, by a tire surface anomaly (e.g. a tread joint) can be within typical uniformity tolerances assessed during tire manufacturing. The local peak of radial run out, however, can generate high harmonics (e.g. harmonics greater than 10) of radial run out for the tire. These high harmonics of radial run out can lead to the excitation of air contributing to cavity noise.
Correction for radial run out caused by surface anomalies can be performed, for instance, by grinding the surface of the tread. This generalized grinding, however, is typically performed to address low harmonics of radial run out and other uniformity parameters for the tire. Moreover in certain circumstances, grinding the tread can create a displeasing appearance to the tread of the tire. In addition, grinding the tread can lead to the creation of other non-uniformity issues, such as the creation of tangential force variation.
Thus, a need exists for a system and method for reducing the harmonic contribution cause by a localized tire surface anomaly due to a tread joint or other tire characteristic. A system and method that can correct for multiple harmonics caused by the tire surface anomaly would be particularly useful. For instance, reduction of multiple harmonics, particularly higher order harmonics, can contribute to a reduction in cavity noise.